Amorphization/templated recrystallization method for hybrid orientation substrates

ABSTRACT

The present invention provides an improved amorphization/templated recrystallization (ATR) method for fabricating low-defect-density hybrid orientation substrates. ATR methods for hybrid orientation substrate fabrication generally start with a Si layer having a first orientation bonded to a second Si layer or substrate having a second orientation. Selected regions of the first Si layer are amorphized and then recrystallized into the orientation of the second Si layer by using the second Si layer as a template. The process flow of the present invention solves two major difficulties not disclosed by prior art ATR methods: the creation of “corner defects” at the edges of amorphized Si regions bounded by trenches, and undesired orientation changes during a high temperature post-recrystallization defect-removal annealing of non-ATR&#39;d regions not bounded by trenches. In particular, this invention provides a process flow comprising the steps of (i) amorphization and low-temperature recrystallization performed in substrate regions free of trenches, (ii) formation of trench isolation regions that subsume the defective regions at the edge of the ATR&#39;d regions, and (iii) a high-temperature defect-removal anneal performed with the trench isolation regions in place.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/871,694, filed Oct. 12, 2007 which is a divisionalapplication of U.S. patent application Ser. No. 11/142,646, filed Jun.1, 2005, now U.S. Pat. No. 7,291,539 and is related to U.S. patentapplication Ser. No. 11/031,142 entitled “Method for fabricatinglow-defect-density changed orientation Si,” filed Jan. 7, 2005, now U.S.Pat. No. 7,285,473, and to U.S. patent application Ser. No. 10/725,850,entitled “Planar substrate with selected semiconductor crystalorientations formed by localized amorphization and recrystallization ofstacked template layers,” filed Dec. 2, 2003. The contents of each ofthe aforementioned U.S. patent Applications are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates to crystalline substrate structures suchas, for example, high-performance complementary metal oxidesemiconductor (CMOS) circuits, in which carrier mobility is enhanced byutilizing different semiconductor surface orientations for p-channelfield effect transistors (pFETs) and n-channel field effect transistors(nFETs). More particularly, the present invention relates to an improvedamorphization/templated recrystallization technique for fabricatingplanar hybrid orientation substrate structures comprising semiconductorswith different surface crystal orientations.

BACKGROUND OF THE INVENTION

Semiconductor device technology is increasingly relying on specialtysemiconductor substrates to improve the performance of the n-channelMOSFETs (nFETs) and p-channel MOSFETs (pFETs) in complementary metaloxide semiconductor (CMOS) circuits. For example, the strong dependenceof carrier mobility on silicon orientation has led to increased interestin hybrid orientation Si substrates in which nFETs are formed in(100)-oriented Si (the orientation in which electron mobility is higher)and pFETs are formed in (110)-oriented Si (the orientation in which holemobility is higher), as described by M. Yang, et al. in “HighPerformance CMOS Fabricated on Hybrid Substrate with Different CrystalOrientations,” IEDM 2003 Paper 18.7 and U.S. patent application Ser. No.10/250,241, filed Jun. 17, 2003 entitled “High-performance CMOS SOIdevices on hybrid crystal-oriented substrates”, now U.S. Pat. No.7,329,923.

Amorphization/templated recrystallization (ATR) methods for fabricatinghybrid orientation substrates such as disclosed, for example, in U.S.patent application Ser. No. 10/725,850, filed Dec. 2, 2003 entitled“Planar substrate with selected semiconductor crystal orientationsformed by localized amorphization and recrystallization of stackedtemplate layers,” typically start with a first semiconductor layerhaving a first orientation directly bonded to a second semiconductorlayer having a second orientation different from the first. Selectedareas of the first semiconductor layer are amorphized by ionimplantation, and then recrystallized into the orientation of the secondsemiconductor layer using the second semiconductor layer as a crystaltemplate.

FIGS. 1A-1D show a “top amorphization/bottom templating” version of theATR method of U.S. patent application Ser. No. 10/725,850 for forming abulk hybrid orientation Si substrate. In this version of ATR, the firstsemiconductor layer being amorphized is on the top and the secondsemiconductor layer acting as a template is on the bottom. Specifically,FIG. 1A shows the starting substrate 10 which comprises a top siliconlayer 20 having a first crystal orientation, a bottom silicon layer orsubstrate 30 having a second crystal orientation different from thefirst, and a bonded interface 40 between them. FIG. 1B shows thesubstrate of FIG. 1A (designated now as 10′) after formation ofdielectric-filled shallow trench isolation (STI) regions 50. Selectedregions of top Si layer 20 are then subjected to amorphizing ion implant60 to produce one or more amorphized regions 70, as shown in FIG. 1C.The amorphizing ion implant 60 would typically be performed with Si orGe ions. Amorphized regions 70 span the entire thickness of the upper Silayer 20, and extend into the lower Si layer 30. The amorphized regions70 are then recrystallized into the second crystal orientation, usingthe lower Si layer 30 as a template, to produce (idealized) planarhybrid orientation substrate 80 with recrystallized, changed-orientationSi region 90. In this example, the orientations of Si regions 30 and 90may have a (100) orientation, while the Si regions 20 may have a (110)orientation.

In contrast to the idealized outcome shown in FIG. 1D, recrystallizationof the amorphized Si region 70 in the structures of FIG. 1C wouldtypically result in the structure of FIG. 2A, with end-of-range defects97 and corner defects 99. End-of-range defects are well studied and havebeen reported in, for example, J. P. de Souza and D. K. Sadana, inHandbook on Semiconductors: Materials, Properties and Preparation,edited by S. Mahajan (North Holland, 1994), Vol. 3b, p. 2033, and cornerdefects have been described previously by N. Burbure and K. S. Jones in“The effect of oxide trenches on defect formation and evolution inion-implanted silicon,” Mat. Res. Soc. Symp. Proc. 810 C4.19 (2004). Asdescribed in U.S. Pat. No. 7,285,473, end-of-range defects 97 remainingafter ATR may be eliminated by including a high temperature(aprroximately 1300° C.) anneal as part of the recrystallizationprocess, as shown in FIG. 2B. However, this high temperature annealingis not expected to be effective in eliminating corner defects 99. Whilemore aggressive annealing (e.g., more than a few hours at temperatureshigher than 1300° C.) might help to a limited degree, it is not apreferred option due to concerns about reaction and dissolution of oxidelayers contained in the STI fill.

FIGS. 3A-3E show the geometry of corner defects 99 in relation to a FETdevice that might comprise ATR'd region 90. Specifically, FIGS. 3A-3Bshow top views of ATR'd region 90 with (FIG. 3B) and without (FIG. 3A)FET 112 including a gate and a gate dielectric. Reference numeral 50denotes the dilectric filled trench region. FIGS. 3C-3E show crosssection views of FIG. 3B through lines C-C1, D-D1, and E-E1,respectively. Corner defects 99 are a particular concern in circledregions 118, where they are directly under the gate and the gatedielectric of FET 112 and may contribute to undesirable leakage.

One could devise methods to repair corner defects 99, but none appear tobe very practical. For example, one could re-amorphize the ATR'd regionsto a shallower depth than the initial amorphization, and thenrecrystallize. This would still leave corner defects, but they would besmaller, since the corner defect size scales with the amorphizationdepth, as discussed in the publication by Burbure and Jones mentionedabove. Alternatively one could remove the corner defect regions andreplace them with an insulator or epitaxially-grown Si. However, thesteps to do this are quite involved. It is therefore clear that thepreferred approach would be to avoid forming corner defects in the firstplace.

Corner defect formation can be avoided with the ATR-before-STI processflow of FIGS. 4A-E. Specifically, FIG. 4A shows a starting substrate 10such as shown in FIG. 1A. FIG. 4B shows the substrate 10 of FIG. 4Abeing subjected to amorphizing ion implant 60 to produce one or moreamorphized regions 120 and non-amorphized regions 20′. Amorphizedregions 120 span the entire thickness of the upper Si layer 20, andextend into the lower Si layer 30. Amorphized regions 120 are thenrecrystallized using the lower Si layer 30 as a template to producechanged-orientation Si region 130 bordered below by end-of-range defects97 and bordered laterally by potentially defective edge regions 140, asshown in FIG. 4C. End-of range defects 97 are then removed by a hightemperature defect-removal anneal leaving annealed edge regions 140′, asshown in FIG. 4D. Annealed edge regions 140′ are then replaced by STIregions 150, as shown in FIG. 4E.

FIGS. 5A-5D, which are provided by the applicants of the presentapplication, show cross-section SEM images of border regionscorresponding to 140 in FIG. 4C for the case of a 200-nm-thick110-oriented Si DSB (direct silicon bonded) layer on a 100-oriented Sihandle wafer. All samples were first coated with Cr, cleaved, and thensubjected to a short Secco etch to highlight interfaces and defects. TheSecco etch includes a mixture of HF, K₂CrO₇, and H₂O. FIG. 5A shows asample after a patterned amorphization with 4E15/cm² 220 keV Ge at asubstrate temperature of 10° C., prior to recrystallization annealing.Amorphized region 155 is bordered below by 100-oriented substrate 157and bordered laterally by non-amorphized 110-oriented DSB region 159.Bonded interface 161 is between Si substrate 157 and a DSB region 159.Non-amorphized DSB regions comprise 5 μm squares (aligned with the 110directions of the 100-oriented substrate) on approximately 10 μmcenters. FIGS. 5B-5C show the sample of FIG. 5A after a 900° C./1 minuterapid thermal recrystallization anneal along two perpendicular cleavescoinciding with the 110 directions of the 100-oriented substrate, onealong the 100 direction of the DSB layer and the other perpendicular toit. Region 163 has recrystallized into the 100 orientation of thesubstrate, separated from the 110-oriented regions by angled interfaces165 and/or 167.

The images of FIGS. 5B-5C make it clear that the orientation-changingATR methods taught in U.S. patent application Ser. No. 10/725,850 canprovide structures including Si regions of different orientationslaterally separated by characteristically angled border regions. Theform and defectivity of these border regions depends on the kinetics ofthe various growth fronts as well as the initial orientation of thecrystal planes from which the recrystallization is templated; forexample, defective region 171 is present in the image of FIG. 5B, butnot the image of FIG. 5C. In view of the possibility that thesecharacteristically angled border regions will have uses not anticipatedor described in the prior art, it is therefore asserted that the hybridorientation ATR methods taught by U.S. patent application Ser. No.10/725,850 may be employed to create Si regions with thesecharacteristically distinctive borders, without departing from the scopeof the original inventive method.

While solving the corner defect problem, the ATR-before-STI approach ofFIGS. 4A-4E unfortunately gives rise to another problem: when therecrystallization and high temperature defect-removal anneals areperformed before STI formation, the non-ATR'd Si regions (or islands)20′ can “disappear” by converting to the orientation of the underlyingsubstrate. FIG. 5D shows a cross section analogous to the one of FIG. 5Cat early stages of this disappearance/conversion process (i.e., after aslow furnace ramp to 1250° C.). The image suggests that (at least forthe case of the 110-oriented islands embedded in a 100-orientedsubstrate) disappearance of non-ATR'd regions proceeds by a gradualbottom corner rounding or erosion rather than by a lateral translationof the edge regions. Interestingly, the stability of non-ATR'd110-oriented Si islands embedded in 100-oriented Si substrates appearsto be a concern only when the edges of 110-oriented islands such as 20′in FIG. 4 are bordered by changed-orientation Si regions 130, since the110-oriented islands 20′ bounded by oxide-filled trenches survive thehigh temperature defect-removal anneals with their original orientationintact.

Another concern with the ATR methods of U.S. patent application Ser. No.10/725,850 is their reliance on ion implantation amorphization as themeans by which the initial orientation information is removed fromregions selected for orientation change. Alternative methods foreffecting such crystalline-to-noncrystalline transformations in theseselected regions would also be highly desirable.

SUMMARY OF THE INVENTION

The present invention provides an ATR method for forming low-defectdensity hybrid orientation substrates which avoids the problems of (i)corner defects in the ATR'd regions, and (ii) undesired orientationchange of the non-ATR'd regions.

Specifically, the ATR method of the present invention comprises firstfabricating a hybrid orientation substrate by the prior art processingsteps described in U.S. patent application Ser. No. 10/725,850. In oneembodiment disclosed in the '850 application, the hybrid orientedsubstrate is formed by: (i) forming a bilayer template stack comprisinga direct silicon bonded (DSB) layer of Si having a first surfaceorientation (for example, a 110 orientation) disposed on an underlyingSi substrate having a second surface orientation (for example, a 100orientation), (ii) amorphizing selected regions of the DSB layer down tothe underlying Si substrate layer to leave a DSB layer with amorphizedand original-orientation regions, and (iii) performing arecrystallization anneal at or below a first temperature to convert theamorphized regions of the DSB layer into regions of changed-orientationSi having the orientation of the underlying Si substrate. Next,insulator-filled shallow trench isolation (STI) regions are formed tolaterally separate the original-orientation and changed-orientationregions of the DSB layer. In accordance with the present invention, theisolation regions extend to a depth that is at least as deep as the DSBlayer thickness. After forming the insulator-filled STI regions, adefect removal anneal is performed at or below a second temperaturehigher than the first temperature, with the STI regions in place,according to the prior art U.S. Pat. No. 7,285,473.

More generally, the inventive method comprises:

providing a hybrid orientation substrate comprising a directsemiconductor bonded layer of a first surface orientation disposed on anunderlying semiconductor substrate having a second surface orientation,wherein selected regions of the direct semiconductor bonded layer areamorphized and subjected to a recrystallization anneal at or below afirst temperature providing selected regions of said directsemiconductor bonded layer having the second surface orientation;

forming a dielectric isolation region to laterally separate the selectedregions of the direct semiconductor bonded layer having said secondsurface orientation from regions of the direct semiconductor bondedlayer having said first surface orientation, wherein the dielectricisolation region extends to a depth that is at least as deep as thedirect semiconductor bonded layer thickness; and

performing a defect removal anneal at or below a second temperaturehigher than said first temperature.

This process flow with STI formation after the amorphization andlow-temperature recrystallization steps but before a defect removalanneal avoids the two problems described above: (i) corner defects wherethe ATR'd regions contact STI, and (ii) the conversion of non-ATR'd(original orientation) DSB layer regions to the substrate orientationduring the high-temperature defect removal anneal. In a slightly morecomplicated variation of this process flow, the trenches of the STIregions are formed before the defect removal anneal and filled with apermanent dielectric after the defect removal anneal, therebyeliminating the requirement that the STI fill be able to survive thedefect removal anneal. In both process flows, the borders of the ATR'dregions adjacent to non-ATR'd DSB regions may contain defects after therecrystallization anneal. However, this is not a problem because thesedefective edge regions are quite localized (typically having a width ofonly about half the DSB layer thickness) and would ordinarily bereplaced by STI.

While the inventive methods above were specifically described for thecase of a Si DSB layer on a bulk Si substrate, they may also beimplemented with other substrates (for example, Si-on-insulator (SOT) orsemiconductor-on-insulator substrates instead of bulk Si substrates),with DSB and substrate layers comprising other semiconductor materials(e.g., Ge, Si-containing semiconductors such as SiGe alloys, thesematerials further including dopants, etc.), and/or with any combinationof strained and unstrained layers.

In addition, the key concepts of (i) avoiding corner defects at Si/STIborders by recrystallizing the amorphized Si before STI formation, (ii)using insulator-filled isolation trenches positioned at the bordersbetween changed-orientation ATR'd regions and original-orientationnon-ATR'd regions to eliminate potentially defective border-region Si,and (iii) preserving the post-recrystallization dimensions of thechanged-orientation ATR'd regions and original-orientation non-ATR'd DSBlayer regions by using STI or STI-like features to laterally separatethese regions from each other during high temperature defect-removalannealing may be generally applied to the many variations of the hybridATR methods described in U.S. patent application Ser. No. 10/725,850without departing from the scope of the present invention. For example,the present invention may be applied to ATR schemes utilizing bottomamorphization and top templating, or schemes in which buried insulatorlayers are created after ATR.

A further aspect of the present invention teaches the use oflaser-induced melting as an alternative or adjunct to ion implantamorphization in forming hybrid orientation substrates. For example,regions of a bilayer template stack selected for an orientation-changingATR treatment as described here and in the original methods of U.S.patent application Ser. No. 10/725,850 may be subjected to a lasermelting process that melts to a depth below the bonded interfaceseparating upper and lower Si layers of different orientations. Theresulting laser-melted regions are then recrystallized from the meltusing the lower Si layer as a template.

More generally, this aspect of the inventive method for forming hybridorientation substrates comprises the steps of: providing a startingsubstrate comprising a direct semiconductor bonded layer of a firstsurface orientation disposed on an underlying semiconductor substratelayer having a second surface orientation, melting and recrystallizingselected regions of the direct semiconductor bonded layer to provideselected regions of said direct semiconductor bonded layer having thesecond surface orientation.

The underlying semiconductor substrate layer may be, for example, a bulksemiconductor wafer or a semiconductor-on-insulator layer.Insulator-filled isolation regions may be formed between the regionsselected for orientation-changing melting and recrystallization andthose not selected for orientation-changing melting andrecrystallization. Additional defect-removal annealing may be performedafter recrystallization, as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are pictorial representations (through cross sectionalviews) illustrating an idealized top amorphization/bottom templatingSTI-before-ATR prior art process for forming a hybrid orientation Sisubstrate;

FIGS. 2A-2B are pictorial representations (through cross sectionalviews) illustrating the types and locations of defects remaining afterthe prior art STI-before-ATR process of FIG. 1;

FIGS. 3A-3E show the geometry of the corner defects in relation to anFET device comprising changed-orientation ATR'd regions through planviews (FIGS. 3A and 3B) and cross sectional views (FIGS. 3C-3E);

FIGS. 4A-4E are pictorial representations (through cross sectionalviews) illustrating an idealized top amorphization/bottom templatingATR-before-STI prior art process for forming a hybrid orientation Sisubstrate;

FIGS. 5A-5D show cross-section SEM images of border regions betweenATR'd and non-ATR'd regions for a hybrid orientation substrate initiallycomprising a 110-oriented Si DSB layer on a 100-oriented Si handlewafer: after amorphization but before recrystallization (FIG. 5A), aftera 900° C. recrystallization anneal (FIGS. 5B and 5C), and after a 1250°C. anneal (FIG. 5D);

FIGS. 6A-6E are pictorial representations (through cross sectionalviews) illustrating the steps of a preferred embodiment of the inventivemethod for forming a low-defect density hybrid orientation substrate;

FIGS. 7A-7K are pictorial representations (through cross sectionalviews) illustrating a “disposable STI fill” variation of the methodshown in FIGS. 6A-6E;

FIGS. 8A-8B are pictorial representations (through cross sectionalviews) illustrating initial and final structures for an SOI version ofthe methods of FIGS. 6A-6E and 7A-7K; and

FIGS. 9A-9F are pictorial representations (through cross sectionalviews) illustrating the inventive method for the case of bottomamorphization/top templating.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in more detail by referringto the drawings that accompany the present application. In theaccompanying drawings, like and corresponding elements are referred toby like reference numerals. It is also noted that the drawings of thepresent invention representing the structures during the variousprocessing steps of the present invention are provided for illustrativepurposes and are thus not drawn to scale.

Reference is first made to FIGS. 6A-6E which are pictorialrepresentations (through cross sectional views) illustrating the stepsof a preferred embodiment of the inventive method for forming alow-defect density hybrid orientation substrate, i.e., a hybridorientation substrate with no corner defects and a low (<10⁷/cm²)concentration of residual end-of-range defects. FIG. 6A shows a startingsubstrate 200 comprising an upper silicon layer 220 having a firstcrystal orientation, a lower silicon layer or substrate 230 having asecond crystal orientation different from the first, and a bondedinterface 240 between them. FIG. 6B shows substrate 200 of FIG. 6A beingsubjected to an amorphizing ion implant 60 to produce one or moreamorphized regions 250 and non-amorphized regions 220′. Although notshown in FIG. 6B, the amorphizing ion implant 60 would typically be ablanket implant and regions 220′ would typically be masked by some typeof photoresist. Amorphized regions 250 span the entire thickness of theupper Si layer 220, and extend into the lower Si layer 230. Amorphizedregions 250 are then recrystallized by an initial recrystallizationanneal to produce changed-orientation Si regions 260 having theorientation of underlying Si layer 230 (which acts as a template).Changed-orientation ATR'd regions 260 are now bordered below byend-of-range defects 270 and bordered laterally by edge regions 280, asshown in FIG. 6C. FIG. 6D shows the structure of FIG. 6C after formationof dielectric isolation regions such as dielectric-filled shallow trenchisolation (STI) regions 290 whose location and dimensions wouldtypically be designed to subsume defective edge regions 280. To preventundesired orientation changes of the original-orientation, non-ATR'dregions 220′ during subsequent high temperature annealing, isolationregions 290 should extend below the interface 240. End-of range defects270 are then removed by a high temperature defect-removal anneal toproduce the hybrid orientation substrate structure 300 of FIG. 6E withlow-defect-density changed-orientation ATR'd Si region 310 and non-ATR'doriginal orientation Si region 220′ with STI region 290 between them.Devices such as FETs and other circuit elements (not shown) would thenbe fabricated on substrate 300 using techniques that are well known inthe art.

Referring to the structure of FIG. 6A, the orientations of Si layers 220and 230 may be selected from 100, 110, 111, and other major and minorMiller indices. For example, in a preferred embodiment of the invention,the upper Si layer 220 can have a 110 orientation and the lower Si layer230 can have a 100 orientation. Alternatively, the upper Si layer 220can have a 100 orientation and the lower Si layer 230 can have a 110orientation.

As discussed in U.S. patent application Ser. No. 10/725,850 and U.S.Pat. No. 7,285,473, the initial recrystallization anneal used to convertthe structure of FIG. 6B into the structure of FIG. 6C may be performedwith any of a variety of prior art recrystallization conditions, suchas, for example, temperatures from about 500° C. to about 900° C.Annealing at temperatures in the range from about 600° C. to about 650°C. in inert ambients for times of about 1 minute to about 2 hours areconsidered particularly preferable. In general, the annealingtemperature should be high enough to produce a reasonable rate ofrecrystallization, yet low enough to ensure that the recrystallizationis templated (rather than spontaneous and random). An additionalconsideration not discussed in U.S. patent application Ser. No.10/725,850 and U.S. Pat. No. 7,285,473 is that the recrystallizationshould be performed under conditions mild enough to preserve theintegrity of the non-ATR'd regions 220′. However, the non-ATR'd regions220′ are expected to be stable at all temperatures in the rangetypically used for recrystallization annealing. Furthermore, somedimensional changes in the non-ATR'd regions 220′ may even be tolerable,since as mentioned above in connection with FIG. 5D, disappearance ofthe non-ATR'd regions 220′ proceeds by a gradual bottom corner roundingrather than by a lateral translation of the edge regions. As a guide toselecting a suitable recrystallization anneal, it is noted thatdetectable corner rounding could be observed in the samples of FIGS.5A-5D after a 2-hour anneal at 1050° C.

Options for the high temperature defect-removal anneal used forconverting the structure of FIG. 6D to substrate structure 300 of FIG.6E are described in U.S. Pat. No. 7,285,473 and incorporated byreference. In particular, it is noted that the defect-removal annealwould typically be performed with a protective cap layer in place and ata temperature in the range from about 1200° C. to about 1320° C. Howeverit should be noted that the high-temperature defect removal anneal mayoptionally be omitted or performed at a lower temperature (e.g., in arange from about 1000° C. to about 1200° C.) if the remaining defects donot adversely affect subsequent device performance and reliability.Interestingly, it has been found that the temperature/time conditions atwhich the end-of-range damage starts disappearing are much the same asthose at which the non-ATR'd regions start showing bottom cornerrounding.

FIGS. 7A-7K show pictorial representations (through cross sectionalviews) of a “disposable STI fill” variation of the method of FIGS.6A-6E. Specifically, FIG. 7A shows the structure of FIG. 6C, formedaccording to the process steps described in connection with thestructures of FIGS. 6A-6B. FIG. 7B shows the structure of FIG. 7A afterdeposition and patterning of a hard mask layer 320, which also functionsas a polish stop. Hard mask layer 320 would typically comprise a thin(on the order of about 5 to about 10 nm) SiO₂ underlayer and a thickersilicon nitride overlayer. FIG. 7C shows the structure of FIG. 7B aftera trench etch to form cavities 330. Cavities 330 are then partially orcompletely filled with one or more disposable dielectrics to form thestructure of FIG. 7D (in which cavity 330 is partially filled withdielectric 340) or FIG. 7E (in which cavity 330 is completely filledwith dielectric 340′). Dielectric 340 protects the hard mask layers 320and sides of the trenches 330 from oxidation during the defect removalannealing. Dielectric 340 is preferably SiO₂ and selectively removablewith respect to the hard mask layer 320. FIG. 7F shows the structure ofFIG. 7D after defect-removal annealing (the details of which werediscussed above in connection with FIG. 6) which removes end-of-rangedamage loops 270. FIG. 7G shows the structure of FIG. 7F after removalof disposable dielectric 340. FIG. 7H shows the structure of FIG. 7Gafter deposition of one or more permanent dielectrics 350 to fill andoverfill the cavity 330. Dielectric 350 is then planarized, stopping onthe polish stop 320 to form the structure of FIG. 7H with filled STIregion 350′. Finally, polish stop layers 320 are removed to form thestructure of FIG. 7J, and STI region 350′ is lightly etched back to formthe structure of FIG. 7K with planar STI region 350″.

While the process flows of FIGS. 6A-6E and 7A-7K are shown for the caseof a Si DSB layer on a bulk Si substrate, the same process flow may alsobe implemented with other substrates (for example, Si-on-insulator (SOI)or semiconductor-on-insulator substrates instead of bulk Si substrates),with DSB and substrate layers comprising other semiconductor materials(e.g., Ge, Si-containing semiconductors such as SiGe alloys, thesematerials further including dopants, etc.), and/or with any combinationof strained and unstrained layers to make any of the structuresdescribed in U.S. patent application Ser. No. 10/725,850.

FIGS. 8A-8B are pictorial representations (through cross sectionalviews) illustrating initial and final structures for the process flowsof FIGS. 6A-6E and 7A-7K exercised on an SOI substrate. FIG. 8A shows astarting substrate 500 comprising a handle wafer 510, a buried insulatorlayer 520, a DSB layer 530 having a first crystal orientation, and anSOI layer 540 having a second orientation different from the first, andFIG. 8B shows a final structure comprising smaller regions 530′ and 540′of the original DSB and SOI layers 530 and 540, STI regions 550 andchanged-orientation ATR'd regions 560.

As mentioned above, the key concepts of (i) avoiding corner defects atSi/STI borders by recrystallizing the amorphized Si before STIformation, (ii) using insulator-filled isolation trenches positioned atthe borders between changed-orientation ATR'd regions andoriginal-orientation non-ATR'd regions to eliminate potentiallydefective border-region Si, and (iii) preserving thepost-recrystallization dimensions of the changed-orientation ATR'dregions and original-orientation non-ATR'd DSB layer regions by usingSTI or STI-like features to laterally separate these regions from eachother during high temperature defect-removal annealing may be generallyapplied to the many variations of the hybrid ATR methods described inU.S. patent application Ser. No. 10/725,850 without departing from thescope of the present invention. For example, the present invention maybe applied to ATR schemes utilizing bottom amorphization and toptemplating, or schemes in which buried insulator layers are createdafter ATR.

In particular, a low-defect-density hybrid orientationsemiconductor-on-insulator substrate may be achieved by utilizing abottom amorphization/top templating scheme comprising the steps of:forming a bilayer template layer stack on an insulating substrate layer,said bilayer stack comprising a first, lower, single crystalsemiconductor-on-insulator layer having a first orientation and asecond, upper single crystal semiconductor layer having a secondorientation different from the first; amorphizing the lowersemiconductor layer of the bilayer template stack in selected areas toform localized amorphized regions; performing a recrystallization annealat or below a first temperature to convert the amorphized regions of thelower semiconductor layer into regions of changed-orientation Si havingthe orientation of the upper semiconductor layer; removing the uppersemiconductor layer of the stack to expose the lower semiconductorlayer; forming insulator-filled shallow trench isolation (STI) regionsto laterally separate the original-orientation and changed-orientationregions of lower semiconductor wherein the isolation regions contact theinsulating substrate layer; and performing a defect removal anneal at orbelow a second temperature higher than the first temperature.

The steps of this process flow are shown in the pictorialrepresentations (through cross sectional views) of FIGS. 9A-9F.Specifically, FIG. 9A shows a starting substrate 600 comprising an uppersilicon layer 610 having a first crystal orientation and a lower siliconlayer 620 having a second crystal orientation different from the first,and a bonded interface 630 between them. Lower silicon layer 620 isdisposed on a buried insulator layer 640 on the substrate 650. FIG. 9Bshows the substrate of FIG. 9A being subjected to an amorphizing ionimplant 660 to produce one or more subsurface amorphized regions 670 andnon-amorphized regions 660′. Although not shown in FIG. 6B, amorphizingion implant 660 would typically be a blanket implant and regions 660′would typically be masked by some type of photoresist. Amorphizedregions 670 span the entire thickness of lower Si layer 620, and extendinto upper Si layer 610. Amorphized regions 670 are then recrystallizedby a recrystallization anneal at or below a first temperature to producechanged-orientation ATR'd Si regions 680 having the orientation ofoverlying Si layer 610 (which acts as a template). ATR'd regions 680 arenow bordered above by “beginning-of-range” defects 690 and borderedlaterally by defective edge regions 700, as shown in FIG. 9C. FIG. 6Dshows the structure of FIG. 9C after removal of the upper Si layer 610by a process such as thermal oxidation/wet etch or chemical mechanicalpolishing. FIG. 9E shows the structure of FIG. 9D after formation ofdielectric isolation regions such as dielectric-filled shallow trenchisolation (STI) regions 720 which would typically subsume defective edgeregions 700.

Beginning-of range defects 690 are then removed by a high temperaturedefect-removal anneal to produce the hybrid orientation substratestructure 750 of FIG. 9F with coplanar low-defect-densitychanged-orientation ATR'd Si region 760 having the first crystalorientation and non-ATR'd Si region 660′ having the second (original)crystal orientation with STI region 750 between them. Devices such asFETs and other circuit elements (not shown) would then be fabricated onsubstrate 750 using techniques well known to those skilled in the art.

The conditions for the recrystallization anneal and the defect-removalanneals for the process flow of FIGS. 9A-9F should be similar to thosedescribed in connection with the process flows of FIGS. 6A-6E. As wasthe case of the process flow of FIGS. 7A-7K, the insulator-filledtrenches of FIGS. 9A-9F may instead be filled or partially filled with adisposable insulator prior to the defect-removal anneal, with thedisposable insulator being replaced with a permanent insulator after thedefect removal anneal.

The observation that high temperature annealing can cause single crystalSi island regions of one orientation embedded in a Si substrate of adifferent orientation to undergo an orientation change that leaves theislands with the orientation of the substrate, was introduced in theBackground section above as both as a primary motivation for the presentinvention and as a problem to be avoided. However, it should be notedthat the same annealing conditions giving rise to this effect may onoccasion be employed advantageously and deliberately to change the size,shape, and/or number of such islands. For example, annealing in certaintemperature ranges can cause bottom corner rounding of the islands, asshown in FIG. 5D, or cause their complete disappearance.

Alternatively, selected islands may be preserved by laterallysurrounding them with protective (filled or empty) trenches prior toannealing at time/temperature conditions sufficient to make theremaining (unprotected) islands disappear.

A further aspect of the present invention teaches the use oflaser-induced melting as an alternative or adjunct to ion implantamorphization. For example, regions of a bilayer template stack selectedfor an orientation-changing ATR treatment as described here and in theoriginal methods of U.S. patent application Ser. No. 10/725,850 may besubjected to a laser melting process that melts to a depth below thebonded interface separating upper and lower Si layers of differentorientations. The resulting laser-melted regions are then recrystallizedfrom the melt using the lower Si layer as a template.

A key issue with laser melting is the requirement that the melt depth(i) extend beyond the bonded interface in regions undergoing anorientation change (to ensure templating from the lower Si layer), and(ii) remain within the upper Si layer in regions not undergoing anorientation change (to ensure templating from the upper Si layer and areturn to the original orientation). These requirements are most easilymet by using blanket laser irradiation with antireflection (AR) coatinglayers atop Si regions where deep melting (and highest absorbed laserfluence) is desired, and no coatings or more reflective layers atop Siregions where shallow or no melting is desired. To minimize lateraltemplating, laser irradiation may be performed after STI is in place.Melt depth control and selectivity may also be improved by using ionimplantation to amorphize the regions to be laser melted, sinceamorphous Si has a melting point several hundred ° C. lower than that ofcrystalline Si and thus can be induced to melt at fluences below thethreshold for melting crystalline Si.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A method for forming a hybrid orientation substrate comprising:providing a starting substrate comprising a direct semiconductor bondedlayer of a first surface orientation disposed on an underlyingsemiconductor substrate layer having a second surface orientation; andmelting and recrystallizing selected regions of the direct semiconductorbonded layer to provide selected regions of said direct semiconductorbonded layer having the second surface orientation.
 2. The method ofclaim 1 wherein the underlying semiconductor substrate layer is a bulksemiconductor wafer or a semiconductor-on-insulator layer.
 3. The methodof claim 1 further comprising forming insulator-filled isolation regionsbetween the regions selected for orientation-changing melting andrecrystallization and those not selected for orientation-changingmelting and recrystallization.
 4. The method of claim 3 wherein saidinsulator-filled isolation trenches are formed before said melting andrecrystallization steps.
 5. The method of claim 3 wherein saidinsulator-filled isolation trenches are formed after said melting andrecrystallization steps.
 6. The method of claim 1 further comprising adefect-removal anneal after recrystallization.